昊天SEO

sed 简明教程

sed全名叫stream editor,流编辑器,用程序的方式来编辑文本,相当的hacker啊。sed基本上就是玩正则模式匹配,所以,玩sed的人,正则表达式一般都比较强。

同样,本篇文章不会说sed的全部东西,你可以参看sed的手册,我这里主要还是想和大家竞争一下那些从手机指缝间或马桶里流走的时间,用这些时间来学习一些东西。当然,接下来的还是要靠大家自己双手。

用s命令替换

我使用下面的这段文本做演示:

$ cat pets.txt
This is my cat
 my cat's name is betty
This is my dog
 my dog's name is frank
This is my fish
 my fish's name is george
This is my goat
 my goat's name is adam
把其中的my字符串替换成Hao Chen’s,下面的语句应该很好理解(s表示替换命令,/my/表示匹配my,/Hao Chen’s/表示把匹配替换成Hao Chen’s,/g 表示一行上的替换所有的匹配):
$ sed "s/my/Hao Chen's/g" pets.txt
 This is Hao Chen's cat
 Hao Chen's cat's name is betty
 This is Hao Chen's dog
 Hao Chen's dog's name is frank
 This is Hao Chen's fish
 Hao Chen's fish's name is george
 This is Hao Chen's goat
 Hao Chen's goat's name is adam

注意:如果你要使用单引号,那么你没办法通过\’这样来转义,就有双引号就可以了,在双引号内可以用\”来转义。

再注意:上面的sed并没有对文件的内容改变,只是把处理过后的内容输出,如果你要写回文件,你可以使用重定向,如:

$ sed "s/my/Hao Chen's/g" pets.txt > hao_pets.txt
或使用 -i 参数直接修改文件内容:
$ sed -i "s/my/Hao Chen's/g" pets.txt

在每一行最前面加点东西:

$ sed 's/^/#/g' pets.txt
#This is my cat
# my cat's name is betty
#This is my dog
# my dog's name is frank
#This is my fish
# my fish's name is george
#This is my goat
# my goat's name is adam

在每一行最后面加点东西:

$ sed 's/$/ --- /g' pets.txt
This is my cat ---
 my cat's name is betty ---
This is my dog ---
 my dog's name is frank ---
This is my fish ---
 my fish's name is george ---
This is my goat ---
 my goat's name is adam ---

顺手介绍一下正则表达式的一些最基本的东西:

^ 表示一行的开头。如:/^#/ 以#开头的匹配。
$ 表示一行的结尾。如:/}$/ 以}结尾的匹配。
\< 表示词首。 如 \<abc 表示以 abc 为首的詞。
\> 表示词尾。 如 abc\> 表示以 abc 結尾的詞。
. 表示任何单个字符。
* 表示某个字符出现了0次或多次。
[ ] 字符集合。 如:[abc]表示匹配a或b或c,还有[a-zA-Z]表示匹配所有的26个字符。如果其中有^表示反,如[^a]表示非a的字符
正规则表达式是一些很牛的事,比如我们要去掉某html中的tags:

html.txt

<b>This</b> is what <span style="text-decoration: underline;">I</span> meant. Understand?

看看我们的sed命令

# 如果你这样搞的话,就会有问题
$ sed 's/<.*>//g' html.txt
 Understand?
 
# 要解决上面的那个问题,就得像下面这样。
# 其中的'[^>]' 指定了除了>的字符重复0次或多次。
$ sed 's/<[^>]*>//g' html.txt
This is what I meant. Understand?

我们再来看看指定需要替换的内容:

$ sed "3s/my/your/g" pets.txt
This is my cat
 my cat's name is betty
This is your dog
 my dog's name is frank
This is my fish
 my fish's name is george
This is my goat
 my goat's name is adam

下面的命令只替换第3到第6行的文本。

$ sed "3,6s/my/your/g" pets.txt
This is my cat
 my cat's name is betty
This is your dog
 your dog's name is frank
This is your fish
 your fish's name is george
This is my goat
 my goat's name is adam
$ cat my.txt
This is my cat, my cat's name is betty
This is my dog, my dog's name is frank
This is my fish, my fish's name is george
This is my goat, my goat's name is adam

只替换每一行的第一个s:

$ sed 's/s/S/1' my.txt
ThiS is my cat, my cat's name is betty
ThiS is my dog, my dog's name is frank
ThiS is my fish, my fish's name is george
ThiS is my goat, my goat's name is adam

只替换每一行的第二个s:

$ sed 's/s/S/2' my.txt
This iS my cat, my cat's name is betty
This iS my dog, my dog's name is frank
This iS my fish, my fish's name is george
This iS my goat, my goat's name is adam

只替换第一行的第3个以后的s:

$ sed 's/s/S/3g' my.txt
 This is my cat, my cat'S name iS betty
 This is my dog, my dog'S name iS frank
 This is my fiSh, my fiSh'S name iS george
 This is my goat, my goat'S name iS adam

本节课就写到这里

下节更精彩

 

 

 

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